Rear Attachment Lens Positive Image-Side Element Aberration Correction
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Solution Overview
Problem
In mirrorless cameras, achieving favorable image plane characteristics with a rear attachment lens is challenging due to the short back focus of the master lens, which requires a rear attachment lens with negative refractive power, leading to increased Petzval sum and difficulty in correcting aberrations such as field curvature and chromatic aberrations.
Innovation Solution
A rear attachment lens is designed with a positive lens closest to the image side, having a convex lens surface towards the image side, and arranged to satisfy specific conditional expressions that allow for a longer focal length and improved refractive power arrangement, facilitating the correction of Petzval sum and aberrations, even with a short back focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a rear attachment lens with negative refractive power is used to extend focal length, then the focal length of the entire system increases, but the Petzval sum increases in negative direction and image plane characteristics deteriorate
Solution Approach 1:
The patent inverts the conventional configuration by placing a positive lens closest to the image side instead of a negative lens. This positive lens has a convex surface toward the image side, which is the opposite of the traditional rear attachment lens design. This inversion allows the Petzval sum to be corrected while still achieving focal length extension through the overall negative refractive power of the attachment lens system
Solution Approach 2:
The patent changes the refractive power parameter of the lens closest to the image side from negative to positive. By making this parameter change and satisfying specific conditional expressions regarding focal length and principal point positions, the system achieves both focal length extension and improved image plane characteristics through better aberration correction
2Length of stationary object
If the back focus of the master lens is short, then the structure is more compact, but it becomes difficult to correct aberrations and achieve favorable image plane characteristics
Solution Approach 1:
The patent addresses the short back focus constraint by operating in another design dimension - using a positive lens with convex surface toward the image side and carefully controlling the principal point positions. This dimensional change in design approach allows aberration correction despite the limited space
Solution Approach 2:
The patent changes key optical parameters including the refractive power of the image-side lens and the positions of principal points to satisfy specific conditional expressions. These parameter changes enable effective aberration correction even with the constrained short back focus distance
3Manufacturing precision
If a positive lens with convex surface toward image side is used, then the Petzval sum can be corrected and image plane characteristics improve, but the design complexity increases
Solution Approach 1:
The patent applies local quality by making only the lens closest to the image side have a positive refractive power with a convex surface toward the image side, while other lenses in the attachment lens system can have different configurations. This localized change achieves Petzval sum correction without requiring complete redesign of the entire lens system
Solution Approach 2:
The patent changes specific parameters of the positive lens including its focal length, principal point positions, and surface curvatures to satisfy conditional expressions. By controlling these parameters within specific ranges, the system achieves good image plane characteristics without excessive design complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables the rear attachment lens to effectively extend the focal length of the entire system, improve image plane characteristics, and correct aberrations, ensuring high optical performance by adjusting the refractive power and principal point positions.
Implementation Method 1
A rear attachment lens is designed with a positive lens closest to the image side, having a convex lens surface towards the image side
Implementation Method 2
The rear attachment lens making the focal length of the entire system longer than the focal length of the master lens alone generally has a negative refractive power. Having this refractive power, the rear attachment lens enlarges an image to be formed
Data Source
AI summary
A rear attachment lens according to the aspect of the embodiments is configured to vary a focal length of a system by being attached to an image side of a master lens. The rear attachment lens includes a positive lens arranged closest to the image side in which a lens surface on the image side of the positive lens has a shape convex toward the image side. A focal length of the rear attachment lens, a magnification of the rear attachment lens when attached to the master lens, and a distance from the lens surface on the image side of the positive lens to a rear principal point position of the rear attachment lens when attached to the master lens are appropriately set.